JUST WATCHED

Bloodiest suicide bombing shocks Yemen

MUST WATCH

Bloodiest suicide bombing shocks Yemen01:29

PLAY VIDEO

A Yemeni official in Washington said it was too early to know who was responsible but that suicide attacks are "the hallmark of al Qaeda."

The partially lawless Middle Eastern country has become a central battleground in the fight against al Qaeda, with the terror network's leader calling recently for an uprising against the new president.

Gen. Ammar Saleh was sacked as director of the National Security Bureau, said a Yemeni official who is not authorized to speak to the media. He is being replaced by Maj. Gen. Mohammed Jameh al-Khadar.

Saleh may keep a second and more important post as first deputy for national security.

The head of central security, Abdul Malik al-Tayyeb, was fired by presidential decree after the attack. He is being replaced by Fadhl al-Qosi.

The soldiers were preparing for Tuesday's National Day of Unification ceremonies when they were attacked.

The day celebrates the union of South Yemen and North Yemen on May 22, 1990, to form Yemen.

U.N. Secretary-General Ban Ki-moon condemned the attack and called for the perpetrators to be held accountable.

"The secretary-general calls on all in Yemen to reject the use of violence in all its forms and manifestations, and expects them (to) play a full and constructive role in implementing Yemen's political Transition Agreement," a statement from his office said.

"So, Ali Abdallah Saleh is gone, and his successor Abed Rabbo Mansour Hadi has taken over," al Qaeda's chief commander Ayman al-Zawahiri said in a video posted on jihadist forums.

Saleh, who led Yemen for 30 years, relinquished power last year after an extended popular uprising in a transition agreement that was supported by the United States. Hadi was Saleh's vice president, and al Qaeda has exploited the connection to stir resentment against the new government.

Last year, Ansaar al-Sharia, an offshoot of al Qaeda, took over the majority of districts in the southern Abyan province, benefiting from the political turmoil in the country. Numerous military bases were evacuated, making it easier for the militant groups to grow in power and territory.

On Sunday, fierce clashes between government troops and al Qaeda fighters left 21 people dead, two local security officials said.

The officials said the violence erupted when hundreds of troops attempted to sweep through areas around the district of Jaar, the main stronghold for al Qaeda in Abyan province.

Al Qaeda fighters fought back, kicking off clashes that continued for nine hours, the officials said. Fourteen militants and seven troops were killed in the fighting, they said.

Government forces have been battling fighters loyal to the local branch of al Qaeda for more than a year, but not made lasting headway.

The United States has carried out dozens of drone strikes against militants in Yemen, including the radical American-born cleric Anwar al-Awlaki, who was killed in September.

U.S. officials said last month they had foiled a plot to bring down a U.S.-bound aircraft with a device that originated in Yemen.

The plot was brought to authorities' attention by a mole who infiltrated al Qaeda, a source in the region told CNN.

The mole works for Saudi intelligence, which has cooperated with the CIA for years, the source said.

Information from the mole also led to a drone strike this month that killed Fahd al Quso, 37, whom the U.S. considered a senior operative of al Qaeda in the Arabian Peninsula.